The overall concern for the quality of the environment has raised renewed interest in the manner in which various chemicals are synthesized, refined, stored, and used, Specifically, there is a growing concern regarding the manufacture, storage, and distribution, as well as with the waste generated during retail storage of such materials.
For example, hydrocarbon fuels such as gasoline and household fuel oil are often stored in tanks which are buried at central distribution points or at retail service stations. During storage, transport, and sale of these materials, tank leaking or spilling often occurs, creating an area of environmental contamination which may ultimately prove hazardous.
One common means of alleviating the environmental hazard is removing and disposing of this contaminated soil in a landfill. However, landfill disposal of this contaminated matter may often be a time consuming and expensive endeavor, as well as being subject to burdensome government regulations.
Contaminated soil may also be treated to remove the hydrocarbon waste through various means. Processes for the thermal remediation of contaminated soil have been developed and refined. For example, Clarke, U.S. Pat. No. 4,420,901 relates to a tractor drawn farm implement for decontaminating fields. Goedhart, U.S. Pat. No. 4,648,332 relates to a fluidized bed furnace for decontaminating soil. Przewalski, U.S. Pat. No. 4,700,638 relates to an apparatus for the disposal of hazardous material such as dioxin and polychlorinated biphenyls through a thermal process.
U.S. Pat. No. 4,815,398 relates to a rotary dryer for thermally decontaminating soils. Gerken et al., U.S. Pat. No. 4,782,625 relates to a materials dryer used to decontaminate soils. Hardison et al., U.S. Pat. No. 4,667,609 relates to an infrared apparatus for thermally decontaminating soils. Other methods of treatment include processing soil in converted stationary asphalt plants. However, these processes are not portable and generally produce a high concentration of particulate exhaust.
U.S. Pat. No. 4,667,609 relates to an apparatus for the treatment of soil contaminated with hydrocarbons, including a sealed negatively pressurized high temperature furnace wherein the multi-zone heater is maintained at about 2900.degree. F.
U.S. Pat. No. 4,202,282 relates to a method and apparatus for processing sewage sludge through the use of infrared radiation under a slight vacuum to capture the noxious odors.
U.S. Pat. No. 4,870,911 relates to an incinerator pyrolyzer for continuously burning waste material in a rotating kiln.
U.S. Pat. No. 5,020,452 relates to a thermal remediation apparatus that includes a condensing system for cooling exhaust gases rendered from a combustion chamber after processing of contaminated soil. The water used in the condensing system does not contact exhaust fumes directly. Particulate material in the exhaust generally falls into a draw off box, with cleaned exhaust being pulled from the condensation system through a fan and into the environment. However, the pollutants present within the exhaust gases which enter into the condensing system may not be sufficiently cleaned using such a condensation system, thereby leaving the problem of possible contaminants escaping from the system into the environment, even after passage through the condensation system and exhaust mechanisms.
Another method for processing the hot gases which result from combustion of a contaminated soil sample is set forth in U.S. Pat. No. 5,195,887. In this system, the hot gases and fines are processed through a dryer system that facilitates separation of the materials in the exhaust into a gas phase and a solid phase. Gases containing uncombusted volatile organic compounds are then directed back to the primary dryer for additional exposure to heat in order to complete combustion. Additional separation of the fines from these gases is achieved in a bag house.
Other separation means described in the art for removing fines contained in exhaust gases from the combustion of contaminated soil include a scrubber or stripper column filled with a liquid or a gas to capture particulate species (U.S. Pat. No. 5,195,887). In this regard, columns filled with carbon are used to absorb fines based on organic residues. The solvent or absorbent used may depend upon the particular species involved. Such processes inherently introduce problems of proper selection and disposal of the liquid Solvent or the carbon absorbent used to trap the captured fines.
The present invention employs a water based system to wash volatilized contaminants rendered from a contaminated soil combustion (unpublished observations). However, problems remained regarding suitable disposal of the resulting contaminated water used, as well as the large volumes of water that would be continuously required to run a water-based vapor washing system.
Disposal of contaminated water may often be a time-consuming and expensive endeavor, as well as being subject to burdensome government regulations. Accordingly, the inventor recognized a need for a self-contained and waste conscious vapor washing apparatus that would enhance the cleaning efficiency of the vapors over that available with "condensing" systems, and that most preferably efficiently would recycle and contain any contaminant isolated from the material being processed in a safe and convenient manner. A system that could decontaminate large quantities of contaminated liquid materials having volatile organic compounds is also a need perceived by the inventor. To date, no thermal-based system for processing industrial sludge is available.
The apparatus and methods described in the aforegoing patents generally utilize expensive and sophisticated machinery to dispose of contaminants such as dioxin and polychlorinated biphenyls (PCBs). Moreover, these mechanisms use high volumes of air, which necessitate a variety of complex exhaust filtering and cleaning systems. Finally, the previously disclosed devices and processes are generally either completely stationary or, alternatively, portable But require the expenditure of extended time, energy, and space in transport and set up.
Accordingly, there is a need for a portable thermal desorption apparatus which is capable of removing contaminants from soil and other particulate and liquid compositions that does not require complex exhaust treatment systems, that is capable of recycling processing materials, such as water, efficiently and quickly, and that may be used at the contamination site with a minimum expenditure of space, set-up time, and energy.